Indian Journal of Chemistry Vol. 36A, August 1997, pp.667-67 I EffectZYXWVUTSRQPONMLKJIHGFEDCBA ofOH-/AI ratio of pillaring solution on the texture and surface acidity of aluminium pillared clays t ParkashKumar, R V JasrarqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA & SGT Bbat" ResearchCentre, Indian PetrochemicalCorporationLimited,Vadodara391 346, India Received 24 February 1997;revised 7 April 1997 A few alumina pillared montmorillonite clay samples have been prepared by varying ORf Al ratio of the crosslinking solution in the range of 1.5 to 1.9. Variations in OR-fAl ratio of cross linking solution has led to the different adsorption capacities of the pillared clays for nitrogen, water, benzene and pyridine adsorption isotherms. Pillared clay intercalated with crosslinking solution with OR-fAI ratio of 1.7 shows highest adsorption capacity for water, benzene and pyridine. The nitrogen adsorption isotherms are of type-I indicating rnicroporosity. Infrared spectra of pyridine adsorbed samples show that pillaring generates Lewis as well Bronsted type of acidity in the clays. After pillaring the number of accessible protons available on the surface of the clay is increased as compared to that in unpillared clay. The porous and thermally stable materials obtained by pillaring of smectite type clays hold a good potential as catalysts and selective adsorbents for separation and purification'r'. Pillaring is essentially an ion exchange process wherein interlayer clay ions are exchanged with inorganic polynuclear cations like Keggin ion [Al\304 (OH)24(H20)12f+ (refs 3, 4). During the synthesis of such pillared clay materials, thorough knowledge of factors like OR/AI ratio, pH of pillaring solution and drying techniques which influence the pillaring process is required. However, few studies are reported showing the effect of such factors on the texture and surface acidity of the pillared clays which play significant role in deciding the adsorption and catalytic properties. In the present work, we report the effect of OR/AI ratio of the crosslinking solution on the texture and surface acidity of aluminium pillared montmorillonite clay.WVUTSRQPONMLKJIHGFEDCBA M aterials and Methods The clay used for pillaring was Na- Montmorillonite SWY-l from Crook county, Wyoming, USA which was procured from source clay repository of the Clay Minerals Society. The clay was used as such without any further modification. Small amounts of impurities in the tlPCL CommunicationNo. 321 form of quartz, calcite and K-feldspar were present' in the clay. The clay had an approximate structural formula of ~.Ol Cao.04Nao.3o)(AlI.54M&.26 Fe o . 2o ) (Si 3 . 93 Alo.d OIO·nH 2 0 and cation exchange capacity value of 85 meq/100 g of clay". The Na-Montmorillonite clay was pillared with aluminium polyoxocations. AlCI 3 .6H 2 0 and NaOH (S.D. Fine Cnemicals, India) were used to prepare hydroxy aluminium oligomeric solution. Preparation of crosslinking solution of hydroxy-AI oligomers involved slow addition of base (0.2rqponmlkjihgfedcbaZYXWVUTSRQ M NaOH) to AICI 3 ·6H 2 0 (0.2 M) at the rate of 0.6 ml/min using microtube peristatic pump (MP-3, Tokyo Rikakai Co., Japan). The base addition was accompanied by vigorous stirring at ambient temperature. The crosslinking solutions with final pH of 4.3 to 4.5 and OR/AI ratio of 1.5 to 1.9 were prepared and clays pillared with respective solutions are given in Table 1. Oligomer containing solution was aged at 50°C for 24 h prior to use. The Keggin type structure of aluminium polyoxocation is reported to consist of central four coordinated aluminium ions surrounded by twelve AlO. octahedra'. Synthesis and drying A dilute aqueous dispersion (1%) of montmo- rillonite clay was prepared by mixing the clay with water at room temperature for 10-12 h. Aged